Acyl desaturase enzymes catalyze the formation of double bonds in fatty acids derived from either dietary sources or de novo synthesis in the liver. Mammals synthesize four desaturases of differing chain length specificity that catalyze the addition of double bonds at the Δ9, Δ6, Δ5 and Δ4 positions. Stearoyl-CoA desaturases (SCDs) introduce a double bond in the Δ9-position of saturated fatty acids. The preferred substrates are palmitoyl-CoA (16:0) and stearoyl-CoA (18:0), which are converted to palmitoleoyl-CoA (16:1) and oleoyl-CoA (18:1), respectively. The resulting mono-unsaturated fatty acids are substrates for incorporation into phospholipids, triglycerides, and cholesterol esters, and also function in gene transcription, and as precursors for other biologically active compounds such as thromboxanes and prostaglandins.
A number of mammalian SCD genes have been cloned. For example, two genes have been cloned from rat (SCD1, 2)1,2 and four SCD genes have been isolated from mouse (SCD1, 2, 3, 4.)3,4 Until now, a single SCD gene, SCD1, has been characterized in humans.5 
Alterations in SCD gene expression and/or enzyme activity have been correlated with disease states. These disease states may fall into two classes: those that are direct effects of decreased SCD enzyme activity and those that have been correlated with changes in SCD activity where the causal relationship between enzyme activity and the disease state is not known.
Mutations in mouse SCD1 cause disturbances in skin lipids, abnormal differentiation of sebaceous glands and go on to develop an alopecia similar to clinical scarring alopecias seen in humans6. In addition, mutants homozygous for a disruption of SCD1 show corneal defects, suggesting that SCD1 is required for ocular barrier function in the eye7. These animals also show striking lipid abnormalities, including decreased levels of liver cholesterol esters and triglycerides, and reportedly increased plasma HDL levels8.
Approximately half of all human patients with coronary-artery disease have a low concentration of high density lipoprotein-cholesterol (HDL-C)24. Clustering studies have shown that high triglycerides, low HDL-C, diabetes, hypertension and hyperuricemia were related to insulin resistance/high insulin levels and central and/or obesity25. Thus, the inventor hereto has recognized that modulation of SCD activity in humans may have an effect on lipid metabolism, and play a role in propensity to develop atherosclerosis and cardiovascular disease.
In accordance with the present invention, there is disclosed herein sequence and gene expression data confirming the existence of an additional SCD gene in humans (hSCD5).